1. Field of the Invention
This invention pertains to drilling apparatus, particularly water jet drilling apparatus, with still greater particularity, to hand held water jet drilling apparatus for drilling hard materials, such as, rock.
2. Description of the Prior Art
In mining and quarrying operations it is often desirable to drill holes in rock or other hard substances. The holes are used for placement of explosives or for various types of bolts used for supporting the roof of a tunnel. Several types of approaches have been made to create the tools required for such drilling.
Mechanical drills have commonly been used for drilling holes in mining applications. In the most common type of drill, a drill rod is repeatedly impacted to drive the drill against the rock. There is commonly a slight twisting movement at the same time. The power to impact the drill is commonly applied by compressed air. Drills of this type can cut effectively through hard rock, but produce a large amount of noise and dust. Additionally, a force must be applied to the drill to keep the bit in contact with the rock. This force is not insignificant and often requires a mechanical holder or feed for the drill.
Difficulties with the impact type of drill have led to the development of various types of rotary drills. Those drills operated on the same principle as a twist drill, or are similar to the rotary bits used in oil and gas drilling. In this type of drill, a rotating bit is held against the rock face, and a hole is bored. This type of drill produces a lower volume sound than the impact drill, but still must be held against the rock with a significant force.
Both impact and rotary drills often have a provision for flushing of the hole drilled by a fluid. The fluid may be water or a drilling mud, or even compressed air. The fluid is used to clear the hole and remove chips, and does not function as a cutting tool. Additionally, the fluid can aid in cooling the bits. While the use of a fluid reduces dust, the noise and force problem of conventional drills are not affected.
In all mechanical type drills there is a bit that is in contact with the rock. Such bits are subject to wear and require frequent replacement. Additionally, the current equipment contributes in some degree to the safety problems in mining, as such drills require exposed, rapidly moving parts, which may present a hazard.